This invention relates generally to tufting apparatus for producing patterned textile goods such as carpet, upholstery, and the like, and more particularly to tufting apparatus having a fabric shifting apparatus for moving backing material transversely between pairs of spaced apart hollow needles to which a plurality of yarns are selectively fed, the backing material being shifted in a sequence which precludes a visible line of demarcation in the product at the interface of stitches produced by adjacent needles.
U.S. Pat. No. 4,549,496 which issued Oct. 29, 1985, to Kile discloses highly advantageous tufting apparatus for producing patterned tufted goods using yarns of different colors or different textures. This apparatus is capable of placing yarn into a backing to create patterns and designs which previously were generally available only from a weaving loom or by using printing techniques. The patented apparatus employs multiple heads spaced across the width of a backing material. Each head comprises a reciprocating hollow needle or backing opener tube for penetrating the backing and for implanting yarn tufts in the backing by feeding yarn through the needle pneumatically. The needle is connected to a yarn exchanger into which a plurality of yarns of different colors, for example, are supplied, and a mechanism is included which enables the selection of one or more of the yarns for implantation into the backing for each penetration by the needle. The multiple heads are stepped in synchronism across the backing for a distance corresponding to the spacing between the heads in order to implant a transverse row of yarn tufts. The backing is then advanced to the position of the next row and the process is repeated to implant the next row. A computer controls the selection of the yarn implanted by each backing opener for each penetration of the backing in order to produce a desired pattern in the finished goods.
A significant factor influencing the production speed of practical apparatus embodying the invention of the Kile patent is the number of tufting heads embodied in the apparatus. The greater the number of heads, the less distance each head must traverse and, accordingly, the faster a row of tufts can be implanted in the backing. As the number of heads increases, however, other problems arise. The increased weight makes it more difficult to move the heads accurately and to maintain their alignment and positions relative to one another. Thus rather than the multiple heads which carry the hollow needles being moved across the backing, Ingram U.S. Pat. No. 4,991,523 discloses the backing rather than the heads being shifted transversely to move substantially less weight transversely. This not only simplifies the transverse shifting apparatus but also provides greater speed and accuracy to the yarn placement.
The shifting of the backing material results in a number of transversely spaced stitches produced by each needle, the spacing between adjacent stitches or tufts being equal to the stitch gauge of the product produced. For example, if the needles are spaced apart by two inches and the gauge or space between adjacent stitches is 1/10 inch, the backing is shifted a total of 20 steps from the first penetration of the backing by a particular needle to the last penetration of the backing by that needle before the fabric is shifted in the opposite direction. It was proposed in the prior art apparatus such as that disclosed in the aforesaid Ingram U.S. patent, to shift the backing the required number of steps laterally or transversely while the backing was stationary in the longitudinal or feed direction through the machine. That is, while the lateral shifting steps were made there was no feeding of the backing by the feed rollers through the machine, the feeding only occurring after the last stitch was made by each needle in a particular lateral row. The fabric was thereafter fed one forward move and then shifted a plurality of moves laterally in the opposite direction, a penetration occurring after each lateral shift. Thereafter the fabric was fed one forward move and shifted in the original lateral direction a plurality of moves.
With this shifting sequence the joint or interface between stitches made by adjacent needles is visible. The joint between adjacent needles is particularly apparent in a product where a pattern is produced in a plain or solid background at such interface. In that case a line readily can be seen at the interface and this detracts from the aesthetics of the product.